Spinal Anatomy Study Guide

• Study notes on the spinal cord, brain stem, vasculature and relevant anatomy
• The notes also cover radiculopathy, reflexes, and regional brainstem landmarks

Spinal anatomy

• Gross anatomy and vasculature are key study topics
• Spinal column and disc herniation need to be understood
• Spinal cord and spinal segment divisions are important
• Fiber tracts are essential for understanding sensory and motor pathways
• Spinal reflexes show basic brain behaviour

Spinal Cord Segments

• Cervical spinal cord segments include C1-C8 and are enlarged
• Thoracic spinal cord segments are T1-T12
• Lumbar spinal cord segments L1-L5 are enlarged
• Sacral spinal cord segments are S1-S5
• Coccyx spinal cord segment is Co1

Spinal cord segment definition

• Possesses a dorsal sensory root, dorsal horn, and intermediate gray matter
• Contains a ventral motor horn and ventral root involved in motor function
• Has dorsal, lateral, and ventral columns that transmit different types of information

Spinal Cord Features

• Spinal cord segments trail behind the vertebral column from T1 to Coc1
• Meningeal dura, arachnoid, and denticulate ligaments stabilize the spinal cord in the subarachnoid space
• The Cauda Equina consists of spinal nerves in the lumbar cistern, from L2 to Coc1
• Conus Medullaris marks the end of the spinal cord
• Pia mater extends as the Filum Terminale Internum
• Meningeal dura extends as the Filum Terminale Externum

Vertebrae Features

• Articulating processes create nerve foramina
• Contain epidural fat, Batson’s venous plexus, and the dural sac which surrounds the spinal cord
• Inter-vertebral discs have a nucleus pulposus and annulus fibrosus
• Ligaments include the Ligamentum Flavum, interspinous ligament and posterior longitudinal ligament

Spinal Cord Injuries

• Radiculopathy is where a nerve root exits above the vertebrae, with lateral herniation
• Lumbosacral radiculopathy is where a nerve root exits below vertebrae, with central, lateral, and posterolateral herniation
• Lumbosacral disk herniation presents with unilateral back pain, left lower leg paresthesias, numbness, decreased sensation, and Achilles tendon reflex
• Cervical disk herniation results in unilateral neck pain, left arm pain, decreased arm strength, and numbness in the thumb and index finger

White matter (columns)

• The posterior funiculus carries sensory information
• The lateral funiculus contains both sensory and motor tracts
• The anterior funiculus also transmits sensory and motor information

Gray Matter

• Reed’s Laminae I-X represents the organization of gray matter Sensory areas are located in the dorsal horn
• Motor areas are located in the ventral horn

Fiber tracts

• Gracile and cuneate fasciculi form the dorsal columns and are part of the Dorsal Column Medial Lemniscus (DCML) for sensory information
• Lissauer’s tract handles pain and temperature sensations
• Anterolateral spinothalamic tracts are part of the Anterolateral System (ALS), also for pain and temperature
• Spino-cerebellar tracts transmit unconscious proprioception to the cerebellum
• Lateral corticospinal tract (LCS) is for motor control
• Anterior corticospinal tract (ACS) plays a role in motor function
• Rubrospinal tract is involved in motor coordination and muscle tone

Neurons and Nuclei

• Dorsal horn contains the substantia gelatinosa and Reed’s laminae, processing sensory information
• Ventral (anterior) horn contains Reed’s laminae and is for motor neurons
• Lateral (intermediate) horn contains Clarke’s nucleus involved in proprioception

Sensory Afferent Fibers

• Heavily myelinated proprioceptive fibers in the lateral division of the posterior root; terminate in laminae III-V, VII, MNs and are involved in touch and proprioception (GSA)
• Less myelinated exteroceptive fibers in the middle division of the posterior root, terminate in Lissaeur’s tract or laminae I-V, carry pain and temperature sensations (GSA)
• Interoceptive fibers in the medial division of posterior root, terminate in laminae I, V-VII, carry visceral sensory information from autonomic ganglia (GVA)
• Motor efferent fibers are:
  • Somatic efferents that supply myelinated skeletal muscles and spindles, found in MNs of laminae VIII, IX (GSE)
• Visceral efferents supply visceromotor ganglia in MNs of intermediate zone, lamina VII (GVE)

Spinal cord arterial Supply

• Vertebral artery branches give rise to the anterior and posterior spinal arteries, and arterial vasocorona
• The arteries include central and sulcal arteries
• Segmental arteries give rise to medullary and radicular arteries
• The Great Radicular Artery of Adamkiewicz is a major source of blood supply to the lower spinal cord

Spinal Venous Drainage

• Veins include anterior, posterior, and lateral spinal veins, and anterior and posterior radicular spinal veins
• Venous drainage occurs via the anterior and posterior internal and external plexus, and venous vasocorona

Spinal reflexes

• Myotatic stretch reflex, nociceptive reflex, and crossed extension reflex
• In muscle stretch, myotatic deep tendon reflex
• Reciprocal inhibition prevents competing behavior
• Autogenic inhibition prevents Golgi tendon reflex
• Withdrawal (flexor, nociceptive) reflex
• Crossed extension reflex

Brain divisions

• Brainstem consists of the midbrain, pons, and medulla
• The basilar region contains long fiber tracts and cranial nerves (CNs)
• The tegmentum contains reticular nuclei and fibers
• The midbrain, or tectum, consists of the Corpora Quadrigemina
• Midbrain, pons, medulla have cranial nuclei and nerve components

Notable Brainstem Regions

• Midbrain tectum contains Corpora Quadrigemina (superior and inferior colliculi)
• Pontine, medullary, and midbrain tegmentum contains nuclei, the reticular system, and fiber tracts
• Medullary basis contains pyramids (LCS decussation), brachium pontis, crus cerebri (cerebral peduncle)

Brain Stem Landmarks

• Medulla / pons junction contains cranial nerves VI, VII, VIII, brachium pontis, and pyramids
• Pons / midbrain junction contains cranial nerve IV, brachium pontis, and cerebral peduncles
• Midbrain / thalamus junction contains cranial nerve III and mammillary bodies, + posterior commissure

Brainstem Regions and their anatomical features

• Medulla is defined via Pyramids, Olive, and Tubercles/Trigones
• Midbrain consists of colliculi and mammillary bodies
• Pons is made of Cerebellar Peduncles

Key Brainstem Structures

• Cerebral aqueduct connects the third and fourth ventricles
• Anterior medullary velum and caudal tela choroidea form the 4th ventricle roof
• The 4th ventricle floor is a rhomboid fossa
• Hypoglossal and vagal trigones
• Important components include the sulcus limitans, striae medullaris, superior and inferior fovea, and vestibular area
• Other Foramina of Luschka, Foramen of Magendie, gracile tubercle, cuneate tubercle, and facial colliculus